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Abstract

We present an approach to build multiwavelength achromatic metasurface that can work in off-axis configuration with an ultra-wide applicable incident angle range for visible light. The metasurface is constructed by combining multiple metallic nano-groove gratings, which support enhanced diffractions for transverse magnetic polarization in an ultrawide incident angle range from 10° to 80° due to the excitations of localized gap plasmon modes at different resonance wavelengths. To achieve the achromatic diffraction, the ratio between the resonance wavelength and the period of each elementary grating is fixed. Incident light at those multiple resonance wavelengths can be efficiently diffracted into the same direction with near-complete suppression of the specular reflection. Based on the similar approach, we also design a wide-angled off-axis achromatic flat lens for focusing light of different wavelengths into the same position. Our findings provide an alternative simple way to design various off-axis achromatic flat optical elements without stringent angle requirement for imaging and display applications.

Figures (7)

(a, b) Schematic of the (a) on-axis narrow-angled and (b) off-axis wide-angled achromatic deflection by a metasurface (orange). (c) Schematic of formation of the ultrawide-angled achromatic metasurface by combining multiple metallic nano-groove gratings with different periods (p0, p1, and p2) and groove heights (h0, h1, and h2). The elementary gratings support the near-total diffraction in the −1st order at different wavelengths (λ0, λ1, and λ2) due to the excitation of the localized gap plasmon mode in the nano-grooves with different heights (h0, h1, and h2).

(a) The −1st diffraction efficiency (shown by color bar) of an elementary grating for varying groove height h and incident wavelength λ, when a TM polarized plane wave incidents the structure with angle 45°. The ratio of wavelength and period of the grating is fixed as λ/p = 1.1. (b) The −1st (solid), 0th (dashed) diffraction efficiencies (R-1, R0) and the absorption A (dot-dashed) for three elementary gratings (g0, g1, and g2), whose geometry parameters are indicated by blue circle, green square, and red triangle, respectively, in (a). (c) The field patterns (|Hz|2) at the peak position of R-1 of the three elementary gratings. (d-f) The −1st diffraction efficiency (shown by color bar) of the three elementary gratings, respectively, as a function of incident wavelength and incident angle.